The present invention relates to an intraocular lens for the correction of visual disorders.
According to xe2x80x9cIntraocular Lenses,xe2x80x9d authored by Dr. David J. Apple, published by Williams and Wilkins, 1989, evidence of the concept of intraocular lenses dates back at least two centuries. An 18th century oculist named Tadini proposed the idea of a lens implant and even attempted the development of one. The first recorded implant was by Casaamata around 1795, which failed due to inadequate fixation of the implant to the surface of the eye. The first successful series of implants is credited to Dr. Harold Ridley of London. Ridley observed fragments of an acrylic plastic material used in World War II fighter canopies lodged in the eyes of fighter pilots he treated. Finding no biologic reaction, he chose to use this rigid material for his first intraocular lens implants. A clinical quality version of the material, polymethylmethacrylate (PMMA), more commonly known as Plexiglass, was fabricated by Rayners of London into the first synthetic intraocular lenses (IOL).
Inflammation was commonly observed as a major complication when these early lenses were used. Ridley, however, considered moderate postoperative inflammation to be beneficial because it created adhesions to affix the lens implant. Factors which contributed to the development of postoperative inflammation included residues on or in the lenses of the sterilizing compounds, disinfectants, polishing residues on or in the lenses of the sterilizing compounds, disinfectants, polishing compounds, or additives which were added to control polymerization, as well as rough or sharp edges, holes, or ridges on the intraocular lens itself. Poor lens design suppressed the growth of IOL""s until the design improved and the market grew rapidly in the 1980""s.
According to xe2x80x9cIntraocular Lens Implantationxe2x80x9d by Dr. Emanuel S. Rosen, et al., published by The C. V. Mosby Company, 1984, intraocular lens implant procedures are used primarily for the correction of cataracts, a disease that affects the clarity of the natural lens. For the lens of the eye to remain functional it must maintain its shape and transparency. The embryonic lens is formed by layers of epithelial cells that elongate, form a crystalline structure and become optically clear. This formation process slows down but continues throughout life. The process can be upset by a number of environmental insults including old age, chemical contamination or physical injury. Any of these can trigger the formation of crystalline structures that occur within the lens itself. The newly formed crystalline structures scatter light and destroy the transparency of the lens. In cataract treatment, the IOL replaces the natural lens.
Intraocular corrective lenses for the treatment of refractive errors is a logical evolution of the cataract replacement IOL technology. Corrective lenses (eyeglasses, contact lenses) have been the mainstay for the correction of visual acuity defects. Myopia (nearsightedness), hyperopia (farsightedness), astigmatism and presbyopia (loss of near vision due to factors such as natural lens inflexibility) can all be treated with eyeglasses and contact lenses. Phakic lenses are ones which are used in combination with, rather than in place of, the natural lens in the eye. However, the use of phakic IOLs has generally been unsuccessful due to design related issues that cause insult to the natural lens resulting in such complications as cataracts or abrasion of surrounding tissue.
Refractive surgery is an alternative for treatment of certain types of visual acuity defects. Radial keratotomy (RK) and photorefractive radial keratectomy (PRK) are useful in treating mild to moderate myopia of 6 diopters or less and have shown limited success in treating astigmatism. The effectiveness of these procedures is less predictable in patients with higher degrees of myopia and cannot be used to treat hyperopia or presbyopia. Neither procedure is without significant postoperative events. The hyperopic shift and corneal instability following radial keratotomy and the high incidence of postoperative corneal haze, halos and starbursts with PRK are well documented in the literature. Additionally, both procedures produce overcorrection (hyperopia) and undercorrection (residual myopia) in a significant number of patients. Laser intrastromal in situ keratomilieusis (LASIK) is a new refractive surgery procedure that, in an experienced surgeon""s hands, can treat both low and high degrees of myopia, hyperopia and astigmatism. Preliminary data indicate that LASIK produces few postoperative visual events, postoperative vision stabilizes rapidly compared to RK and PRK, and LASIK does not appear to produce any residual weakening in endothelial structure.
The phakic IOL fills the gaps in refractive surgery treatment modalities for visual acuity defects of all types, including astigmatism and, potentially, presbyopia, assuming that the shortcomings, discussed above, can be dealt with effectively. Such lenses are indicated for any level of myopia or hyperopia, including correction beyond 6 diopters.
The basic concept of phakic IOLs was disclosed in U.S. Pat. No. 4,585,456, Blackmore, issued Apr. 29, 1986. Blackmore describes a phakic lens which is placed on the surface of the natural lens and centered by being held in the ciliary sulcus. This approach failed to provide safe and effective treatment due to such complications as insult to the natural lens causing cataracts, abrasion of the pigment of the iris causing angle closure glaucoma and pupilary block glaucoma caused by blocking the flow of the eye""s aqueous fluid through the pupil. Fixation of the lens using the interaction of the haptics and the ends of the ciliary sulcus requires proper measurement of the eye and selection of the proper haptic size (diagonal dimension across the lens and haptic). Improper haptic size can result in decentration of the implanted lens which leads to improper vision. See also, Mazzocco, et al., Soft Implant Lenses in Cataract Surgery, Slack, Inc., 1986, p. 93, Model E (a phakic lens fitting in the ciliary sulcus). Several other corrective lens implants having stiffened or rigid haptics, such as those described in U.S. Pat. No. 5,258,025, Fedorov, et al., issued Nov. 2, 1993, and U.S. Pat. No. 5,078,742, Dahan, issued Jan. 7, 1992, can result in similar complications. These complications are documented by Fechner, et al., in the Journal of Cataract and Refractive Surgery, March, 1996, vol. 22, pp. 178-81. Fechner also makes the observation that a cataract can form where the intraocular lens is in contact with the natural lens. Sustained contact between the implanted lens and natural lens can insult the natural lens by starving it of oxygen or nutrients provided in the aqueous fluid of the eye resulting in formation of a cataract. See also, U.S. Pat. No. 4,769,035, Kelman, issued Sep. 6, 1988, which discloses a phakic intraocular lens which sits directly on the anterior surface of the natural lens.
PCT/SU88/00180, assigned to Mikrokhirurgiya Glaza, published Apr. 21, 1993, discloses an anterior chamber lens that also has proven to result in significant complications when used. This lens has a means for iris centration that requires the lens to protrude into the anterior chamber; a spool-shaped surface on the lens restricts the movement of the iris. This concept also limits the optical diameter of the lens. The design places all or part of the lens surface in the anterior chamber of the eye and the edges of the spool scatter light creating haloes in the patients vision even during periods of bright ambient light. Also, restricting the movement of the iris results in pigment abrasions and potential trauma to the iris. The maximum diameter or diagonal dimension measured across the optic and haptics is small (less than 10.5 mm) because it is not necessary for the haptics to be centered by the ciliary sulcus or the ciliary zonules since the spool-shaped edges of the optic body are centered in the pupil of the eye by the iris.
A corrective lens that sits on the natural crystalline lens and uses the curvature of the natural lens to center the optic body is disclosed in U.S. Pat. No. 5,480,428, Fedorov et al., issued Jan. 2, 1996. This lens is made from inflexible materials and requires surgical insertion without substantial deformation of the haptic or the optic bodies, thus requiring an incision and suturing to close it. The approach requires a port or hole in the optic body to allow flow of the eye""s aqueous fluid. Surgeons have overcome complications related to blocking the pupil by creating a hole in the iris (an iridotomy) to permit the natural flow of the eye""s aqueous fluid from the posterior chamber to the anterior chamber of the eye.
It would be highly desirable to develop a phakic intraocular lens which did not have the problems associated with the prior art lenses. The present invention overcomes these problems by:
(1) allowing the lens to float freely in the aqueous solution of the eye""s posterior chamber;
(2) providing haptics that can move and flex with the anatomy of the eye;
(3) using a self-centration means that does not abrade or restrict the movement of the iris;
(4) providing haptic bodies in combination with the optic body that capture the natural flow of the aqueous fluid of the eye to create a fluid layer between the implanted lens and the natural lens; and
(5) assisting the circulation of the aqueous fluid of the eye between the natural lens and the implant by utilizing the movement of the iris.
The present invention is a phakic, intraocular corrective lens for the correction of visual disorders such as myopia, hyperopia, astigmatism and presbyopia. The invention comprises an optical body and one or more haptic bodies. The optical body has a lens for the refraction of light at an appropriate optical power to correct a visual disorder. The refractive lens can be negative or positive. The haptic bodies are of such size and shape that they cannot contact the outermost circumference of the ciliary sulcus at the same time (i.e., the lens is not held in place at the ciliary sulcus by the haptic bodies).
The invention is made of a biocompatible, elastomeric material, such as silicone, with a very smooth surface that will not abrade or insult the eye or provide areas where leukocytes and other deposits can collect. The invention may also be made of polymethylmethacrylate, polyhydroxyethylmethacrylate, collagen/acrylic blends and other materials which may be hydrophobic, hydrophilic or gas permeable. The implanted lens floats in the posterior chamber of the eye without touching the natural lens, permitting the implanted lens to move when very small forces are applied to it.
The haptic body(ies) included in the present invention are generally nonplanar with substantially uniform thickness and a shape that approximates the curvature of the natural lens or are substantially spherical. The haptic body(ies) assure that the lens cannot be grossly decentered in the pupil of the eye by making contact with the periphery of the posterior chamber in the area of the ciliary sulcus if such decentration occurs. The haptic(s) is preferably flexible in the direction of the optical axis of the lens so that it will follow the changing radius of the natural lens as the eye accommodates to focus on near or far objects.
The lens of the present invention further includes one or more annular surfaces that protrude from the anterior surface of the lens such that the annular surface is in the path of the iris as it dilates and constricts to adjust the aperture or pupil of the eye for variations in ambient light. Contact by the moving iris places a centering force on the protruding annular surface(s) to move and maintain the lens centered in the pupil of the eye. When the lens is centered, and as the iris continues to constrict, the protruding annular surface(s) is shaped so as not to prevent movement of the iris but rather to allow it to slide over the protruding surface. The protruding surface(s) is contoured, radiused, or beveled to assure that it does not abrade the iris as this sliding takes place. The protruding surface(s) can either be part of the optical body or can be a separate portion of the lens. The surface(s) can be parallel to the optical axis of the eye or ramped to assure that the iris can slide up (in the anterior direction) and over the optical body of the lens.
The annular protruding surface(s) described above must be of such size, shape and location that its entire surface is within the pupil of the eye when dilated at its maximum aperture. The maximum aperture is achieved in the dark, each night as the patient sleeps, or when dilation is achieved by medication. If the lens becomes decentered beyond the maximum aperture of the pupil, the protruding annular surface will act to decenter the lens rather than to center it. Therefore, to assure the protruding annular surface is appropriately centered, the haptic body(s) reaches into the periphery of the posterior chamber of the eye to prevent gross decentration. A similar action occurs with positive lenses where the convex anterior surface of the lens itself protrudes to receive the centering force applied by the iris as it constricts.
The constricting and dilating action of the iris acts on the protruding annular surfaces to move the optic and haptic bodies of the lens to create or assist in the flow and circulation of the eye""s surrounding aqueous fluid such that oxygen and nutrients in the said fluid reach the natural lens.
There is great utility and commercial value for corrective lenses that are implantable in the posterior chamber of the eye to correct visual acuity defects, but the complications which accompany the use of such devices have prevented past attempts from being successful. The present invention overcomes these complications by permitting the lens to float freely in the aqueous solution of the eye rather than being held in place by the haptics or other fixation methods such as by contact between the posterior of the lens and the curvature of the natural lens or fixation in the ciliary sulcus. A free floating, implanted lens will maintain a layer of aqueous fluid between it and the natural lens by capturing the natural flow of the aqueous fluid of the eye to bias the implanted lens away from the natural lens (i.e., unlike many prior art lenses, the lens of the present invention does not rest directly on the natural lens). The low frictional force created by allowing the lens to float freely permits lens centering forces to be applied to the lens by the iris via the protruding annular surfaces described. The present invention allows the lens to be self-centered rather than requiring that it be held in place by spring loaded haptics, flexible haptics, stiffened haptics, rigid haptics, by adhering to the natural lens or other structures of the eye, or by other fixation methods. The net result is a phakic intraocular lens which provides optical correction without damaging the delicate structures of the eye.
Other objects and advantages of the invention will become more apparent from the following specification taken in conjunction with the figures herein. These figures are intended to be exemplary and not limiting of the present invention.